perf_counter: per event wakeups

By request, provide a way to request a wakeup every 'n' events instead
of every page of output.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Orig-LKML-Reference: <20090402091319.323309784@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 06a6fba..5428ba1 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -145,7 +145,7 @@
 				__reserved_1   : 53;
 
 	__u32			extra_config_len;
-	__u32			__reserved_4;
+	__u32			wakeup_events;	/* wakeup every n events */
 
 	__u64			__reserved_2;
 	__u64			__reserved_3;
@@ -321,6 +321,7 @@
 	int				nr_pages;
 	atomic_t			wakeup;
 	atomic_t			head;
+	atomic_t			events;
 	struct perf_counter_mmap_page   *user_page;
 	void 				*data_pages[0];
 };